Sometimes there is confusion about IgnoreUnknownClients. There are two settings that control the behavior of the DHCP server with respect to unknown clients: ConfigureUnknownClients and IgnoreUnknownClients. ConfigureUnknownClients controls whether an unknown client gets an entry automatically generated in the INI file based on IPPOOLs and so on. What makes a client a known client is any kind of client section in the INI file. This can be a client section with wildcards. This client section does not need to contain any IPADDR entry. The IPADDR entry is generated automatically. IgnoreUnknownClients controls how the DHCP server behaves in cases in which no client section is generated by the DHCP server. Sent a NAK to the requesting client or simple ignore the request. Example:

[00-40-8C-??-??-??] ; support only clients with mac address starting with 00-40-8C
AutoConfig=1
[Settings]
ConfigureUnknownClients=0
IgnoreUnknownClients=1

This tells the DHCP server to configure only clients with mac address 00-40-8C-??-??-?? and do not respond to any requests from other kind of clients.